Manufacture of permanent magnets



Patented Jan. 7, 1941 UNITED STATES MANUFACTURE OF PERMANENT MAGNETS Franz Pc'ilzguter, Bochum, Germany, assignor to Siemens & Halske, Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany No Drawing. Application August 3, 1936, Serial In Germany August 7, 1935 3 Claims. (01. 175-21) My invention relates to the manufacture of permanent magnets .consisting of alloys having a particular great coercive force and a strong remanent. magnetism.

Alloys of this kind are well known in the art, the favorable magnetic properties of which are based upon the fact that the hardening elements are segregated within the structure of the alloy in a finely divided state. This hardening is attained by a heat treatment or by controlling the cooling'down of the fused mass. Alloys of iron and tungsten as well as of iron and molybdenum thus treated have already been employed in permanent magnets. It has been further found that also certain nickel-aluminum alloys with or without the addition of W, Mn, Mo, Cu, Cr or C0 pre- I sent excellent magnetic properties. Furthermore, steel alloys for permanent magnets have been employed which contain besides nickel and cobalt a higher percentage of titanium. Moreover, attempts have already been made to employ also'admixtures of Cu, W, Mo, Cr, Al, As, V, Mn in the last-mentioned alloys, the content of each metal in such alloys being up to 20%.

With such high-grade alloys it was possible to attain various favorable values'as to the coercive force and remanence, which may be particularly high in the case of magnetic steels containing titanium. However, the optimum values with alloys containing titanium could be only obtained in laboratories by taking particularly precautionary measures. 'But, in quantity production of such alloys for permanent magnets the values were lower and differed from one another in the individual fused charges.

It is an object of my invention to considerably improve the magnetic properties of the alloys containing titanium as compared to the values hitherto attained.

A further object of my invention consists in rendering uniform the magnetic properties of the different charges of magnetic steels containing titanium so as to attain the optimum values of the properties also in quantity production and to reduce the losses due to rejection.

According to the invention the magnetic properties will be improved and at the same time alloys more suitable for the manufacture of permanent magnets will be obtained if--when employing iron, nickel, cobalt and titanium for the manufacture of permanent magnets-the percentage of cobalt and titanium is kept within predetermined and more precisely within relatively narrow limits and if at the same time the aluminum added thereto has an amount which is brought into a certain ratio to the percentage of titanium. In general, it has been found that the properties are improved and rendered more uniform if the alloys contain about one third, i. e. to 36% cobalt and an equally large amount of iron, whereas the remainder contains nickel, titanium and aluminum in such quantities that the percentage of nickel is more than twice the titanium content, but the aluminum content is smaller than the latter.

The same satisfactory results with different fused masses may be obtained if the percentage that of titanium, but more than 50% of the amount of titanium In general, it is advisable to add an amount of aluminum of 60 to 80% of the titanium content.

With an alloy of Percent C0 35. Ti 8 Al 6' the following values of the magnetic properties have been obtained:

Remanence Br=6150 Coercive force H=902 (B. H.) max.=1,800,000

Small quantities of Mo, W, Cr, Cu, U, V, Zr, Mn, possibly also in amounts to be considered only as impurities may favorably influence the magnetic values.

To obtain the best magnetic properties a certain heat treatment is, in general, necessary. To this end, the above-mentioned alloy is, depending upon its composition, more or less rapidly cooled down from a temperature above 1000 C. Thereupon, the material is annealed at a temperature lying between 500-700 C. Sometimes by the selection of suitable cross-sections or by the use of chill molds or of heat-conducting iron bodies in molding sand, it is possible to impart to the material the most favorable magnetic values by merely coolingit down in the mold. Obviously,

the best magnetiovalues are obtained, if the heat. treatment of the alloy is performed in such a' manner that the hardening elements segregate in the interion bf the entire alloy in a finely divided manner.

When preparing the alloy the observance of the proper percentage of aluminum which is smaller than that of any of the other main constituents may be diflicult. If all constituents are brought together in a cold state and then fused various constituents fuse later than aluminum. Aluminum must, consequently, be kept for a longer time at a temperature which is higher than the fusing point thereof. Owing to its afllnity to oxy-.

gen a portion of the aluminum oxidizes. This loss of metal by oxidation must be taken into consideration when preparing the alloy. How-. ever, the quantity of the oxidized aluminum may be reduced to a minimum by separately melting the entire amount of aluminum to be used or only a portion thereof and by pouring it together with the other constituents previously melted in a separate container. .In this case, the aluminum need be kept only at its melting temperature until it is poured together with) the other constituents. Preferably, the highly refractory constituents, such as iron and nickel are poured into the crucible containing the fused aluminum. By weighing the crucible with the aluminum contained therein when pouring the other constituents the quantity to be poured into the crucible may be easily controlled. In case the alloy should contain further small quantities of other metals besides the above mentioned, such quanfiuctuate within certain limits.

tities may be added, depending upon their proppart somewhat from the above-indicated values,

it beingin most cases doubtful whether the departures are real oi'id'ue to the analysis.

I claim as my invention:

1. A permanent magnet consisting of an alloy containing about 35%, cobalt, 33% iron, 18% nickel, 8% titanium and 6% aluminum.

2. A permanent magnet consisting of an alloy containing 30 to 36% cobalt, above 16% but not more than 20%nickel, 6 to 8% titanium, aluminum in a quantity of 60 to 80% of the titanium content, and the balance substantially iron.

3. A permanent magnet consisting of an iron alloy containing 30 .to 36% cobalt, 16 to 20% nickel, 6 to 10% titanium, aluminum in a quantity of 0.6 to 0.8 of the titanium content, and the balance of iron, and being age-hardened by 0 quenching and annealing.

FRANZ P6LZGUTER. 

